My bike asks for 10w-40, would it be a bad idea to use those 15w-40's you mentioned?If your dad doesn't want to pay a lot of money, he could get Mobil Delvac 1300, or Shell Rotella. These are both HDEO's and are 15W-40's. Excellent additive packages in both and a 4L jug is in the $15-$17 range.
My bike asks for 10w-40, would it be a bad idea to use those 15w-40's you mentioned?